I wanted to install an L-TWOO GRT 12speed Derailleur on a UDH bike. But the UDH has a little groove that prevents the installation as the hanger bolt can not be tightened without the hanger going sideways, hope you get what I mean based on the picture.
A washer would solve the problem I guess… or filing down that groove? Why is it there in the first place…
I would rather say that the derailleur is incompatible with the hanger.
SRAM specifies that there clearance for the derailleur contact surface should be Ø23mm and Shimano specifies Ø20mm.
Without a UDH hanger in front of me to measure, I’d assume the distance from the center of the M10 derailleur hanger thread to that lip must be at least 11.5mm. This is assuming the hanger you have is a SRAM hanger and not a third party manufacured hanger.
Thus my conclusion is that LTWOO has made the OD of the ring that contacts the hanger larger than what both SRAM and Shimano specify for compatibility.
For reference, a SRAM derailleur I have here measures just over Ø19mm and would fit just fine on that hanger.
This is why it’s important for component and frame brands to check the specs and references from established manufacturers to ensure the widest possible compatibilty. It appears LTWOO disregarded this step when designing their derailleur interface.
As a workaround I’d opt to file down the lip instead of using a washer.
A washer will put the derailleur more outboard and may result in not enough leeway to adjust the cage limits to allow shifting to the largest cog(s) on the cassette.
Thanks for this details! Very interesting.
So I’ve measured the outer Ø of the ring (that touches the lip) on the Derailleur and it measures 21.8mm for the Ltwoo.
My guess then is that this specific UDH hangers design is a bit off then?
Possibly.
The LTWOO design is also outside of the norm compared to both SRAM and Shimano.
The latest Shimano RDs have an OD of 20mm there - in line with their spec. document.
As long as the derailleur is not also hitting the frame (looks very tight in the photo) shaving down that lip won’t hurt the hanger.
I’m pretty sure it’s the hanger, as looking at my own MTB and pictures of a genuine SRAM replacement UDH, the change in thickness is more of an abrupt step, rather than a chamfer.
I also think it’s the hanger… in that I have run Ltwoo on a UDH frame with no issues at all.
